WASHINGTON -- Sens. Elizabeth Warren and John McCain, along with two other colleagues, introduced legislation Thursday to reinstate the Glass-Steagall prohibition on federally insured banks from also operating as investment banks.

The legislation would minimize the risk of future goverment bailouts by forcing banks some still consider "too big to fail" to become smaller.

Warren (D-Mass.), an outspoken liberal, and McCain (R-Ariz.), a conservative who was his party's 2008 presidential nominee, are an unlikely pair.

But they are united in the belief that separating traditional deposit-taking from investment activities would reduce risk in the banking system and lessen the chance of future bailouts.

The two were joined by Sens. Maria Cantwell (D-Wash.) and Angus King (I-Maine) in introducing the 21st Century Glass-Steagall Act. Sen. Tom Harkin (D-Iowa) proposed similar legislation in May.

Though the new bill is unlikely to pass Congress, it adds to recent bipartisan criticism that the nation's largest banks remain too big to fail and joins other legislative attempts to restrict their size.

The Glass-Steagall proposal comes after federal banking regulators recently finalized new rules on bank capital reserves and this week proposed tougher provisions for the nation's eight largest banks.

Some analysts have said the 1999 repeal of the Depression-era Glass-Steagall Act, which had established a barrier between deposit-taking and investment activities, laid the groundwork for the 2008 financial crisis.

"Despite the progress we've made since 2008, the biggest banks continue to threaten the economy," Warren said. "The 21st Century Glass-Steagall Act will reestablish a wall between commercial and investment banking, make our financial system more stable and secure, and protect American families."

In the wake of the crisis, some lawmakers have tried unsuccessfully to reinstate the barrier. Last year, former Citigroup Inc. Chief Executive Sanford "Sandy" Weill publicly called for such a move.

McCain has been outspoken for several years about wanting to reinstate Glass-Steagall, an unusual position for a Republican. He and Cantwell introduced similar legislation in 2009.

"Since core provisions of the Glass-Steagall Act were repealed in 1999, shattering the wall dividing commercial banks and investment banks, a culture of dangerous greed and excessive risk-taking has taken root in the banking world," McCain said Thursday.

"Big Wall Street institutions should be free to engage in transactions with significant risk, but not with federally insured deposits," he said.

Rep. Marcy Kaptur (D-Ohio) proposed a similar bill in the House in January. It has 69 co-sponsors.